The Heck Reaction of N-Protected Vinylglycines with 4-Iodoanisole

Abstract

Among N-protected and unprotected vinylglycines tested, N-(benzyloxycarbonyl)vinylglycine (1c) provided the highest yield of the coupling product 3c in the reaction with 1-iodo-4-methoxybenzene (2) in N, N-dimethylformamide in the presence of palladium acetate, sodium bicarbonate, and tetrabutylammonium chloride, whereas none of the desired product was obtained in the reaction with 4-methoxyphenyl trifluoromethanesulfonate (7). The stereoselectivity of the reaction was reversed by employing triethylamine instead of sodium bicarbonate to furnish (Z)-3c predominantly. In the presene of sodium bicarbonate, replacement of the solvent by water improved not only the chemical yield and stereoselectivity but also the optical purity : geometrically pure (E)-3c of 96% ee was formed in a good yield.